This invention relates to dental restorations made from ceramics, glass-ceramics as well as ceramic-matrix and polymer-matrix composite materials using solid free-form fabrication methods. The invention further relates to bodies fabricated by solid free-form techniques which can provide the matrix or skeleton of dental restorations that can be further or concurrently filled with biomimetic substances. The invention also is directed to the manufacture of shells used in the manufacture of dental restorations whereby the shells are manufactured using solid free-form fabrication methods. The invention further relates to the manufacture of models used in the manufacture of dental restorations whereby the models are manufactured using solid free-form fabrication methods.
The fabrication of current all-ceramic dental restorations often requires extensive labor and time and the proficiency of highly skilled technicians. Many state-of-the-art dental restorations reveal a sense of artistry that can typically only be achieved manually or xe2x80x9cby hand.xe2x80x9d While aesthetics are preserved with this process, microstructural inhomogeneities may appear, affecting strength and reliability. The industry has attempted to automate this process by, for example, pressing crowns. Although pressable crowns reduce some of the skill time required, about two hours of concerted effort is necessary to complete a crown. Pressed crowns may also suffer from similar strength and reliability problems typical of xe2x80x9chand madexe2x80x9d crowns.
Computer assisted design/computer assisted milling (CAD/CAM) processes and equipment have been recently introduced into the dental industry. In these processes, a three-dimensional image of a tooth to be restored is created along with the teeth surrounding the tooth in an effort to create a dental restoration which is to be placed over the tooth. This image is displayed on a computer screen. Based on the tooth and surrounding teeth, the dental technician may then select a tooth from a plurality of tooth forms stored in the computer to best fit the tooth to be restored. The selected tooth is projected onto the tooth to be restored until an optimum positioning and fit of the dental restoration is achieved. The digital data concerning the dental restoration thus formed are supplied to a numerically controlled milling machine operating in three dimensions. The milling machine cuts a blank of metal or porcelain material into the dental restoration design based on the data supplied.
Commercially available systems such as CEREC(trademark) from Siemens, PROCERA(copyright) from Nobel Biocare AG, and CICERO(copyright) from Cicero Dental Systems, have attempted to reduce labor and increase structural reliability. However, the necessary machining steps limit the choice of materials that can be used in dental restorations and sometimes compromise the strength and/or aesthetics of the finished restoration.
One of the current limitations of the CAD/CAM approach, which is not easy to overcome, is the fact that currently available systems at best produce copings that require veneering layers to provide a natural appearance. Consequently, final processing of the crown is still in the hands of dental technicians which may limit the resulting structural reliability of the restoration. The existing commercial CAD/CAM systems are unable to produce full crowns. Some of the systems can machine inlays/onlays from a solid ceramic block and are not able to produce crowns or even copings. Others produce copings that make a core of the crown that can fit on the prepared tooth but require additional work by dental technicians to provide final shapes and esthetics. This entails manual building and firing of porcelain layers on top of a coping received from the CAD/CAM facility. Supposedly, one or more systems will be able to automate forming of successive veneering layers of porcelain on top of a CAD/CAM coping which will involve sintering of consecutive porcelain layers following their forming by machining or pressing. This is an automation of steps that are otherwise performed by dental technicians and very well may not be practically advantageous.
One of the key limitations intrinsic to CAM methods is the fact that machining is not competitive technology for mass production of parts and components of any kind including dental restorations, e.g. dentures and crowns. At any given period of time one cutting tool can be used to machine only one part and can not be concurrently used to machine another part.
It is desirable that the automation of the manufacture of dental restorations be conducive to mass production of restorations. It is beneficial that the automation of the manufacture of dental restorations be efficient and useful for a variety of materials.
These and other objects and advantages are accomplished by the process herein directed to solid free-form (SFF) fabrication of dental restorations. Among solid free-form techniques, dimensional printing and fused deposition modeling are preferred because both ceramic and resin-based composite dental restorations can be produced in solid (e.g. denture teeth) or multilayered form (e.g. crowns). Three-dimensional printing is most preferred for mass-production of dental restorations.
Three-dimensional printing is used to create a dental restoration by ink-jet printing a binder into selected areas of sequentially deposited layers of powder. Each layer is created by spreading a thin layer of powder over the surface of a powder bed. Instructions for each layer may be derived directly from a CAD representation of the restoration. The area to be printed is obtained by computing the area of intersection between the desired plane and the CAD representation of the object. All the layers required for an aesthetically sound restoration can be deposited concurrently slice after slice and sintered/cured simultaneously. The amount of green body oversize is equivalent to the amount of shrinkage which occurs during sintering or curing. While the layers become hardened or at least partially hardened as each of the layers is laid down, once the desired final shaped configuration is achieved and the layering process is complete, in some applications it may be desirable that the form and its contents be heated or cured at a suitably selected temperature to further promote binding of the powder particles. The individual sliced segments or layers are joined by one or more binders to form the three dimensional structure. The unbound powder supports temporarily unconnected portions of the component as the structure is built but is removed after completion of printing.